1. Field of the Invention
The present invention relates to a device that allows sections of rigid pipe to be rotatably joined together in such a manner that a swivel connection is formed, and, more particularly, to an improved swivel joint which is suitable for high pressure service and which has a longer service life than do existing devices.
2. Background
Pipe is used in many types of industry, including the oil industry and ship and rail loading industries. The majority of pipe used is rigid pipe. If flexibility is desired, the traditional method is to employ flexible hose. However, flexible hose is expensive and may break due to wear. An alternative to flexible hose is the use of swivel joints. Swivel joints allow two sections of rigid pipe to be joined together in a rotatable fashion. In other words, the sections of joined pipe may turn or twist. Thus, when coupled to elbows and the like, rigid pipe may be manipulated through the use of swivel joints in such a way as to provide a complex passageway.
Swivel joints are not new in the art, but they have traditionally been plagued with problems of leakage, breakdown, and a difficulty in swiveling. Most swivel joints include inner and outer, or male and female, conduits connected with ball race and bearing assemblies to allow for rotation of the conduits while preventing axial movement. An end seal, generally in the form of an O-ring, is provided to close off the space between the outer end of the female conduit and the base of the male conduit. An inner seal is usually provided at the inner junction of the male and female conduits in an attempt to provide added leak protection.
Efforts have been made to increase the leak resistance of prior art swivel joints by providing improved seals to facilitate fluid tight integrity of a swivel joint, such as are disclosed in U.S. Pat. Nos. 2,927,805; 3,347,570; and 4,693,500. But, despite the improvements made in the seals of the prior art devices, problems of leakage, breakdown, and difficulty in swiveling remain. It must be first recognized that the seals of the prior art devices are solely for the purpose of fluid control and containment. When the seals wear, a spill occurs. Furthermore, when the ball races wear more stress is imparted to the seals causing fatigue and failure. Such is also the case when alignment problems are encountered with the bearing races. Misalignment leads to abnormal wear. This wear on the bearing races can cause catastrophic failure of the joint, including axial displacement. Undo wear of seals also contraindicates the use of the prior art swivel joints in submerged service, where environmental concerns are preeminent. Many of the known devices are also difficult to adapt to standard pipe fixtures.
The above described problems with the prior art devices discourage their use, especially in situations where high pressures will be encountered. Still further, repeated seal fatigue lowers the useable life span of the prior art devices and increases repair costs and down time.